Testing for Small-Scale Biodiesel Quality
Despite broad international usage of biodiesel, and despite the US government’s thorough testing and support thereof, Springboard Biodiesel receives a great many questions about biodiesel fuel and engine compatibility.
ASTM Specifications for Biodiesel
First and foremost, these are the ASTM specifications for biodiesel. If your fuel meets ASTM D6571 specs, then the US government (and Springboard Biodiesel) assures you that it will operate flawlessly in your diesel engine.
However, not many people are in the habit of subjecting every batch or their fuel to ASTM testing – it takes time and it’s expensive. We recognize that nothing can completely replace the confidence given by having a certified laboratory ensure that fuel is up to spec and meets all the appropriate standards. However, we are proud to have designed a small-scale biodiesel processor, the BioPro, that has earned a trusted reputation for repeatable ASTM biodiesel production. Our processors have time and again met all the ASTM specs when sent in to various laboratories, by numerous in-house tests and third parties.
Did I Do it Right?
However, there is always a batch about which you wonder: Did I do it right? Did I follow all the steps correctly? Is this what biodiesel is supposed to look like? To answer that nagging uncertainty, we have outlined a variety of tests that can be conducted by the home biodiesel user to ensure that the fuel that you burn will be of the best quality.
What to look for
Visual inspection
One of the most powerful tools that you can use is the visual inspection. The most important thing to look for in the visual inspection of the fuel is good clarity. One customer that has burned tens of thousands of gallons of biodiesel over the last four years says that before he fills up his vehicles from a batch of fuel, he always makes sure he can read a newspaper through a glass of it. It is important to note that COLOR is not a function of fuel quality. Some fuel may be a deep brown color, but still be very clear and of high quality. Similarly, fuel may be a light yellow color, but if it has poor clarity, it is unlikely to be of a good quality. The visual inspection (which is actually part of the ASTM suite of tests) is an excellent firewall against, excessive free water, free glycerine, soaps, particulates, microbial growth, and a host of other potential problems.
Excessive soap
Arguably, the worst area for fuel to be out of spec in, is soap levels. Excessive soap levels in biodiesel are likely the most common cause of permanent engine damage blamed on biodiesel use. If the fuel contains a high level of soaps, it is very likely that is will result in ash formation which will choke and foul engine components. Due to this fact, the ASTM suite of tests have several tests including sulfated ash, carbon residue, and sodium and potassium levels, designed specifically, to detect high levels of soap in fuel. An inexpensive way for a home user to screen out excessive soap levels in fuel is through the use of the pHlip test. This test is very quick and simple to use and may be purchased at Springboard Biodiesel. If a user wants a more quantitative way to measure the soap content of biodiesel, a soap titration kit will allow him to measure the soap level in parts per million. This kit may be purchased at Utah Biodiesel Supply. And here is a video, Learn How to Test Biodiesel for Soap Content.
Leftover catalyst
Another very dangerous component that is sometimes found in biodiesel is residual catalysts remaining from the reactions. Typically, this will result in an alkaline fuel. Along with this, fuel that is excessively old or that has been treated improperly with ion exchange resins or washed improperly may become acidic in nature. Either of these conditions may result in fuel that is prone to forming insoluble precipitants, polymerizing, or increasing in viscosity. Once again, the pHlip test is able to determine if fuel is either acidic or basic in character and therefore is an extremely useful tool ensuring fuel quality.
Incomplete reaction
Another common problem with biodiesel fuel is due to incomplete reactions. Excessive triglycerides (completely un-reacted oil molecules) will increase a fuel’s viscosity and harm its combustion characteristics. Excessive mono and di-glycerides will have the same effect, with the added downside of holding soaps and water in solution. This obviously has a very deleterious effect to biodiesel quality. Once again, the pHlip test is somewhat successful at picking up mono and diglycerides, which are the most harmful of the three potential components in under-reacted fuel. This test is not effective in detecting quantities of triglycerides.
The 27/3 Test
The 27/3 test is very effective at picking up trace quantities of triglycerides in finished biodiesel. Because of its ease, simplicity, and economy, it has become the default test for reaction completeness in the small-scale biodiesel industry. It has some serious shortfalls, however. One is that it is prone to giving false positives. If the methanol alcohol used in the test is contaminated with even a small quantity of water, or if the temperature of the test apparatus is too cold, or if the biodiesel being tested is made from a large proportion of animal based feedstocks, it is likely to signal that there are triglycerides present when in reality, the level of triglycerides is well within the ASTM specifications. (ASTM calls for a maximum of .24% total glycerin. Depending on other conditions, this may be up to 2.5% triglycerides in the in perfectly acceptable fuel.) At the same time, the test is completely ineffective for picking up trace quantities of monoglycerides, which are much more likely to ultimately cause damage to a diesel engine. This having been said, 27/3 test kits are a useful tool at indicating how complete a reaction has been.
Another tool that may be used for testing the total glycerin present in biodiesel is found at Fleet Fuel Testing. This total glycerin test has been used with some success in the industry although it is rather expensive for home users and only provides a qualitative result.
For a discussion of the importance of various aspects of fuel quality and the standard ASTM specifications therefore, please see the article on this site ASTM and the BioPro.
Frequently asked questions
How can I check homemade biodiesel quality without sending it to a lab?
Start with a visual inspection for clarity, then use simple home tests. Good biodiesel should be clear enough to read a newspaper through a glass of it. Color does not indicate quality: dark brown fuel can be excellent if it is clear, while light yellow fuel with poor clarity is likely poor.
Clarity screens for free water, free glycerin, soaps, particulates, and microbial growth. Follow up with the pHlip test for soap and pH, and the 27/3 test for reaction completeness.
Why is soap in biodiesel harmful and how do I test for it?
Excess soap is arguably the most damaging quality problem and a likely leading cause of permanent engine damage blamed on biodiesel. High soap levels lead to ash formation that chokes and fouls engine components.
The pHlip test is a quick, inexpensive way for home producers to screen out high-soap fuel. For a quantitative result, a soap titration kit measures soap content in parts per million. ASTM testing checks for soap through sulfated ash, carbon residue, and sodium and potassium levels.
What does the pHlip test detect in biodiesel?
The pHlip test screens for several common problems in one quick test: excess soap, fuel that is alkaline from leftover catalyst, and fuel that has turned acidic from age, improper ion exchange treatment, or improper washing. It is also somewhat effective at detecting mono- and diglycerides, the most harmful products of an incomplete reaction.
It does not detect triglycerides (unreacted oil), so pair it with the 27/3 test to check reaction completeness.
What is the 27/3 biodiesel test and how reliable is it?
The 27/3 test is the standard small-scale check for reaction completeness; it is simple, cheap, and very sensitive to trace unreacted oil (triglycerides). However, it can give false positives if the test methanol contains a little water, if the apparatus is too cold, or if the fuel is largely made from animal fats.
A failed test does not always mean out-of-spec fuel, since ASTM allows up to 0.24% total glycerin. The 27/3 test also misses monoglycerides, which are more likely to damage an engine.
Do I need ASTM lab testing for biodiesel made in a BioPro?
Not for every batch, though nothing fully replaces the confidence of certified lab results. Fuel that meets the ASTM D6751 specification will run properly in diesel engines, but lab testing takes time and is expensive, so most small producers rely on visual inspection and home tests.
BioPro fuel has repeatedly met ASTM specifications in in-house and third-party laboratory testing when operators follow the manual and use pure ingredients. Periodic lab testing is a good way to confirm your process.
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